1. Field of the Invention
The present invention relates to a cylinder block of an internal combustion engine integrally having a cylinder head and particularly to a cylinder head-integrated cylinder block having liner portions of cylinders made of reinforced aluminum members with heat resistance and wear resistance and a process for manufacturing the cylinder head-integrated cylinder block.
2. Prior Art
In a conventional internal combustion engine, a cylinder head is fastened to a cylinder block through cylinder head bolts and a gasket is provided between the cylinder head and the cylinder block to seal in combustion gas. In this structure, because the cylinder head bolts receive force of expansion caused by combustion, there is a possibility that sealing in of gas cannot be ensured if fastening force of the cylinder head bolts decreases. When rigidity of the cylinder block is not ensured, stress generated in the cylinder block in fastening may cause deformation of liners against which pistons slide. Furthermore, the number of parts is large, which increases the volume of work in assembly.
Because the above problems were caused by separate structures of the cylinder head and the cylinder block in the internal combustion engine, an internal combustion engine having an integral cylinder head-cylinder block structure was proposed in recent years.
There is an integrally-molded engine having an integral cylinder head-cylinder block structure by using cast iron as disclosed in Japanese Utility Model Application Laid-open No. 60-159857, for example. As material for a casting structure, material using casting aluminum which is lightweight and has cooling effect is known in addition to cast iron.
There is one in which cylinder liners in a cylinder block are formed as separate bodies and are coupled to a lower portion of a cylinder head to form an integral structure as disclosed in Japanese Patent Application Laid-open No. 5-26100. The invention of Japanese Patent Application Laid-open No. 5-26100 prevents deformation of the cylinder liners by fitting lower ends of the cylinder liners projecting from the lower end of the cylinder head into a recessed portion of the cylinder block.
Moreover, in the conventional internal combustion engine with the integral structure, dry liners having wear-resistant inner peripheral faces are inserted into cylinder barrels or inner peripheral faces of the cylinder barrels are directly chrome plated.
The casting aluminum has a problem of insufficient strength at a high temperature and it is necessary to increase a thickness of a combustion chamber portion which receives combustion pressure under a high temperature condition in the internal combustion engine using the casting aluminum. However, in a case of making a device of Japanese Utility Model Application Laid-open No. 60-159857 by using the casting aluminum, weight increases because the thickness of an inner wall of the combustion chamber portion is necessary to be increased for insuring strength in the conventional internal combustion engine.
Although the invention of Japanese Patent Application Laid-open No. 5-26100 has a structure for making up the insufficiency of the strength of the liners, the invention does not solve the insufficient strength at the high temperature at its source. Therefore, it is necessary to increase the thickness of the inner wall of the combustion chamber portion to insure the strength, thereby increasing weight.
Furthermore, if the wear-resistant dry liners are inserted through inner peripheral faces of the cylinder-barrels or the inner peripheral faces are directly chrome plated, the number of parts increases, which increases the volume of work in assembly.